The abnormal erythroid precursors from the bone marrow of a patient with refractory anemia and ineffective erythropoiesis were studied and characterized. Ultrastructural studies in our laboratories of material sent to us from France revealed unusual junctional complexes between aberrant mono- and multinucleated erythroid precursors, and similar seemingly intracellular structures resembling the zipper-like junctions we reported in human leukemic monocytes.